In a bar with a dance floor spreading over 2,500 square feet, not everybody saw the shooter enter the building, filled with hundreds of people.

When the shooter opened fire, some witnesses thought they heard fireworks. But others saw the gunman, including a young man in his 20s who said the gunman walked in and started shooting.

"It was all blink of the eye ..." said the man, who declined to give his name. "Guy with a semi-automatic handgun just walked in the front and started popping rounds off at people. It wasn't really random. He was shooting people up close."

Matt Wennerstron, 20, of neighboring Newburry Park, said he saw the gunman open fire on employees at the front desk. That's when he pulled others around me down underneath a pool table.

Authorities later confirmed Long shot a security guard outside, then other security guards and employees inside the bar.

As shots rang out, several people inside the bar hid inside bathrooms and even crawl spaces in the building's attics. In Wennerstron's case, as he outlines in the video, he took the opportunity to escape with others by throwing bar stools through a window as the gunman reloaded his weapon.

Photos from the scene showed people carrying victims, some with blood on their shirts or bodies, including an image pulled from video of a group of young men carrying a person to get help.

In this image taken from video, a victim is carried from the scene of a shooting, Wednesday in Thousand Oaks. A hooded gunman dressed entirely in black opened fire on a crowd at a the Borderline Bar & Grill holding a weekly college night, killing 12 people and sending hundreds fleeing, including some who used barstools to break windows and escape, authorities said Thursday. The gunman was later found dead at the scene.(Photo: RMG News via AP)

As emergency personnel responded, medical staff began providing treatment to those who were injured and witnesses began giving statements to law enforcement.

An FBI agent talks to a potential witness as they stand near the scene Thursday after a mass shooting at the Borderline Bar & Grill in Thousand Oaks.(Photo: AP PHOTO)

For those who had fled from the bar, they stood on sidewalks, wrapped in blankets embracing one another.

Phone calls and text messages to and from loved ones were being made too. Several people at the bar were students from nearby schools like California Lutheran University, Pepperdine, and California State University Channel Islands.

Parents of students were desperate to know if their children and friends were alright. Many headed to a reunification center to connect with their families, hoping for good news. But heartbreaking news awaited others.

Jason Coffman, center, and his father-in-law Mike Johnston, left, talk to a group of reporters Thursday morning about Coffman's son, Cody Gifford-Coffman. He was killed at the Borderline Bar & Grill in Thousand Oaks.(Photo: ALEXA D'ANGELO/THE STAR)

Jason Coffman said his son Cody, 22, was among those killed at the bar. He spoke with Cody, a former Camarillo High School football player, just before he went out for the night.

“I talked to him last night before he headed out the door,” Jason Coffman said. “The first thing I said to him was, ‘Don’t drink and drive.’ The last thing I said was, ‘Son I love you.’ That was the last thing I said.”

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FBI investigators arrive outside the house of Ian David Long, the shooter in Wednesday's attack on the Borderline Bar & Grill in Thousand Oaks, as they wait to search the residence on Thursday in Newbury Park. Using a smoke bomb and a handgun, the former Marine opened fire during college night at the Borderline Bar & Grill, killing 12 people and sending hundreds fleeing in panic before apparently taking his own life, authorities said Thursday. Authorities said the motive for the attack was under investigation. Richard Vogel/AP PHOTO

FBI investigators arrive outside the house of shooting suspect Ian David Long in Newbury Park on Thursday. Authorities said the former Marine opened fire at a country music bar in Southern California on Wednesday evening. Richard Vogel/AP PHOTO

Ventura County Sheriff Geoff Dean speaks to reporters near the scene in Thousand Oaks on Thursday, where a gunman opened fire the previous night inside a country dance bar crowded with hundreds of people. Officials say the suspect is dead inside the bar. Mark J. Terrill/AP PHOTO

Dozens of motorcycle officers from around the region prepare for the procession carrying the body of Ventura County Sheriff's Office Sgt. Ron Helus' body from Los Robles Regional Medical Center in Thousand Oaks to the medical examiner's office in Ventura. JUAN CARLO/THE STAR

Jason Coffman, center, and his father-in-law Mike Johnston, left, talk to a group of reporters Thursday morning about Coffman's son, Cody Gifford-Coffman. He was killed at the Borderline Bar & Grill in Thousand Oaks. ALEXA D'ANGELO/THE STAR

Ventura County Sheriff's deputies stand outside the house of shooting suspect Ian David Long in Newbury Park on Thursday. Authorities said the former Marine opened fire at a country music bar in Thousand Oaks on Wednesday evening. Richard Vogel/AP PHOTO

This undated photo provided by the Ventura County Sheriff's Department shows Sheriff's Sgt. Ron Helus, who was killed Wednesday, Nov. 7, 2018, in a deadly shooting at a country music bar in Thousand Oaks, Calif. AP

People comfort each other as they sit near the scene Thursday in Thousand Oaks where a gunman opened fire Wednesday inside the Borderline Bar & Grill that was crowded with hundreds of people. Mark J. Terrill/AP PHOTO

In this image taken from video, a victim is carried from the scene of a shooting, Wednesday in Thousand Oaks. A hooded gunman dressed entirely in black opened fire on a crowd at a the Borderline Bar & Grill holding a weekly college night, killing 12 people and sending hundreds fleeing, including some who used barstools to break windows and escape, authorities said Thursday. The gunman was later found dead at the scene. RMG News via AP

Sheriff's deputy speaks to a potential witness as they stand near the scene Thursday in Thousand Oaks, where a gunman opened fire Wednesday inside a country dance bar. He killed 12 people and took his own life. Mark J. Terrill/AP

A forensics team works the scene Thursday, in Thousand Oaks after a gunman opened fire Wednesday inside a country dance bar crowded with hundreds of people on college night, killing 12 people and himself. Mark J. Terrill/AP PHOTO

A forensics team works the scene Thursday, Nov. 8, 2018, in Thousand Oaks, Calif. where a gunman opened fire Wednesday inside a country dance bar crowded with hundreds of people on "college night," wounding 11 people including a deputy who rushed to the scene. Ventura County sheriff's spokesman says gunman is dead inside the bar. (AP Photo/Mark J. Terrill) Mark J. Terrill/AP PHOTO

Police officers stand near the scene Thursday in Thousand Oaks where a gunman opened fire Wednesday inside a country dance bar crowded with hundreds of people on college night. The gunman killed 12 people, including a sheriff's deputy. Mark J. Terrill/AP PHOTO

In this image taken from video police officers and FBI agents run at the scene of a shooting, early Thursday morning in Thousand Oaks. A hooded gunman dressed entirely in black opened fire on a crowd at a country dance bar holding a weekly college night. He killed 12 people before taking his own life. AP PHOTO